The present invention relates to a brake fluid pressure control apparatus used for antiskid control to prevent wheel-lock when the brakes are applied.
One type of known brake fluid pressure control apparatus includes a flow control valve having a casing which has a port communicating with a master cylinder, a port communicating with a wheel cylinder, a port communicating with a variable-capacity reservoir through a normally-closed valve, and a port communicating with the discharge side of a pump that sucks the reservoir-side brake fluid and discharges it. The flow control valve further has a spool slidably provided in the casing to cause the conditions of each port to change between communicating and noncommunicating states.
The spool functions as follows. When it is held in a stationary state by the biasing force of a spool spring when the antiskid control is inoperative, the spool provides communication between the master cylinder communicating port and the wheel cylinder communicating port to transmit the brake fluid pressure from the master cylinder to the wheel cylinder. When the antiskid control is activated, the spool moves to a position for closing the master cylinder communicating port to cut off the communication with the wheel cylinder communicating port, and the spool is maintained in this position by the action of the brake fluid supplied from the pump communicating port.
In this known control apparatus, fluid discharged from the pump is introduced from the pump communicating port through the clearance between the casing and the spool, and is transmitted to the master cylinder through the master cylinder communicating port. Although the amount of this fluid is little, the transmitted discharge pressure may undesirably induce a stroke of the master cylinder, causing uncomfortable pedal kick back.
Further, since the master cylinder communicating port is provided to face perpendicularly to the travel direction of the spool, the master cylinder-side fluid pressure acts on the spool in a direction perpendicular to the travel direction thereof. Accordingly, even if the pump discharge pressure from the pump communicating port acts on the spool in the opposite direction, the spool is pressed against the casing wall from one side owing to the difference between these pressures, so that it becomes difficult for the spool to slide smoothly. Consequently, there may be a slight delay in the response of the antiskid control.